Telemetering system



June 6, 1939. c. F. WALLACE TELEMETERING SYSTEM Original Filed Nov. -25, 1935 2 Sheets-Sheet 1 Tiql INVENTOR. 01M 2 ar m I mad 1; ATTORNEY.

June 6, '1939. F LLA E 2,161,603

TELEMETERING SYSTEM Original Filed Nov. 23, 1935 2 Sheets-Sheet 2 Patented Jane 6, 1939.,

PATENT OFFICE TELEMETERHVG SYSTEM Charles F. Wallace, Westiield, N. 1., amino! to Wallace & Tiernan Products, Inc., Bellevillc, N. 1., a corporation of New Jersey Application November 23, 1935, Serial No. 51,307 Renewed October 19, 1938 Claim.

This invention relates to telemetering systems, that is, electrical systems for reproducing movement proportionally at a distance, or, more particularly, for producing movement or change in 5 position of a member at a receiving station corresponding to change in position of an object at a transmitting station.

The invention has been made especially with the idea of improving telemetering apparatus having at the transmitting and receiving stations motors which are required to be operated at speeds maintained at a substantially constant ratio for driving the transmitting apparatus and the receiving apparatus. The most suitable constant speed motors for the purpose are synchronous alternating current motors requiring sources of supply of alternating current to be available at both the transmitting and receiving stations. In case suitable sources of alternating current are not available at both the transmitting and receiving stations, it has been found necessary heretofore to run an alternating current line in addition to the direct current line between the two stations, or to run lines from a considerable 5 distance to bring alternating current in to the location of the transmitting and receiving instruments.

The object of the present invention is to avoid the necessity for having a power supply available at both the transmitting station and the receiving station, or of running a power line between the transmitter and the receiver separate from and in addition to the line which carries the direct current by which the receiving apparatus is controlled from the transmitter, and

to operate the driving motors of both the transmitter and the receiver from a source of alternating current which is available at one end only or at some intermediate point between the trans- 0 mitter and receiver by transmitting over a single pair of conductors both the alternating current and the direct current by which the receiving apparatus is controlled from the transmitter.

The problem was not merely to supply both alternating and direct current over a single twoconductor line, but to do this with a minimum interference with the time of operation of the relays as well as at a minimum of expense. The transmission of both alternating current and digorect current over the same line requires filters to separate the alternating current and direct current where such separation is necessary. To block the alternating current an inductance is used. To block the direct current a condenser is required. Now, a condenser acts as a storage reservoir for direct current. When the supply of direct current is shut oil at the transmitter, current will continue to be supplied to the receiver from the condenser, although at a progressively decreasing rate. The length of time during which current flows from the condenser at an appreciable rate will depend on the capacity of the condenser. The capacity of the condenser in turn depends on the amount of alternating current that it is required to pass Ill under a given potential drop. If it has to pass a large current, then the capacity of the condenser must be large and the time lag in the drop of the direct current to an inappreciable value is likewise relatively large. These relationships are of great importance in telemetering systems as the proper operation of such systems requires substantially instantaneous drop of the direct current to zero at the end of the flow period. For the above reason the alternating current should be as small as practicable, and it has been found that the time lag of the relays may be reduced to a negligible valueif the alternating current and voltage are so proportioned that the power is not greatly in excess of one watt. For example, if the voltage across the motor is the current should be not greatly in excess of 16.5 milliamperes. If the voltage is lower, the ampereage may be correspondingly higher. Prei.'- erably the power consumption is kept below 300 milliwatts. For example, a current of not over 5 milliamperes at 60 volts is suitable for the purposes in view. If telephone lines are used the maximum allowable voltage at any part of the line is 120.

These current and voltage limits may be readily observed by using a motor of the type shown in my U. S. Patent No. 1,995,270. The motors described in said patent are of the resonance type 1 and operate on an alternating current with a speed proportional to the frequency of the current and are self-starting and highly eflicient. Motors of this type can be economically constructed to give the necessary power to operate f telemetering apparatus with a power input of from 1 to 3 milliamperes at 60 volts and if somewhat higher costs are permissible they can by refinements in design and materials be made to operate at very much lower power inputs. On the '1. 5' other hand, for average commercial purposes motors consuming as much as 1 watt sometimes prove to be the most economical compromise as to cost versus efllciency. I

Withrespecttoexpenseoiinstallatmitmay 1'5,

be pointed out that the transmitter and receiver are frequently several miles apart. This has heretofore made it necessary to provide a low resistance line employing relatively heavy and expensive conductors or else required the application of high voltages in order to supply the amount -of power required by the small synchronous alternating current motors which have heretofore been available and suitable for use as the driving motors of telemetering systems. In case normal voltages are employed such low resistance lines mean heavy wires or else a very limited range. If in the other case high line voltages are employed in order to overcome line losses they will usually be in excess of the maximum considered as safe to impress on telephone and similar circuits such as are normally used for telemetering purposes. It can be readily seen that a low capital expenditure can only be accomplished by such means as will allow the use of conductors of small cross section such as the existing types of telephone lines normally used for intercommunicating purposes.

A telemetering system according to the present invention comprises a two-conductor line which carries both alternating current and direct current, both supplied preferably from a single source of alternating current, means for variably interrupting or otherwise controlling the direct current at the transmitting station, indicating apparatus at the receiving station controlled by the direct current, and a driving motor at one or both of the stations driven by the alternating current in said line and which operates on a power input of notgreatly in excess of 1 watt.

The small self-starting synchronous alternating current motors such as have heretofore been used in electric clocks and for operating small instruments require with 60 volts across the motor terminals a current of about milliamperes to give the necessary power for operating telemetering apparatus. If, therefore, the source 01' alternating current has a potential of 120 volts, the connecting line supplying such a motor cannot have a resistance in excess of 667 ohms, otherwise the motor voltage will be below 60 volts or the current supplied will be under the required 90 milliamperes.

With a source of alternating current at 120 volts and a motor such as I use, taking' two milliamperes at 60 volts, the line resistance may be as high as 30,000 ohms. Therefore, with the same size and kind of wires in the transmission line in each case, the length of line with the resonance motor could be 45 times as great as the length of line with the usual synchronous motor. Conversely, with equal lengths of line, the wire for the line supplying the resonance motor could have the cross-sectional area of the wire for a line supplying the usual synchronous motor.

In the accompanying drawings:

Fig. 1 shows diagrammatically a telemetering system according to the invention;

Fig. 2 is a diagrammatic showing of a modification of the circuit arrangement; and

. Fig. 3 is an end view of the transmitting apparatus looking from the right of Fig. 1;

Fig. 4 is a view of the receiving device looking from the right of Fig. 5 and partly in section on line 4-4 of Fig. 5;

Fig. 5 is a side view of the receiving apparatuslooking from the left of Fig. 5 and sectioned on line 6-6 of Fig. 5.

The embodiment of the invention shown by Fig. 1 includes a transmitter A and a receiver B. The receiving device has an indicating member H00 in the form of a pen arm which serves as an indicating pointer and also to make a record mark by pen on a record disk |0I carried by suitable support, which, when the apparatus is in operation, is slowly rotated at a predetermined constant rate by any suitable clock mechanism as customary in recording devices of this general kind.

The transmitting device is located adjacent to the surface of a body of water, the changes in level of which are to be transmitted to and indicated by the receiving device. The body of Water is indicated at 2. A float 3, floating at the surface of the water, is suspended from a sheave 4 by means of a flexible cable 5, which, as shown, passes over the sheave and carries at its other end a counterbalancing weight 6. As the float rises or falls, the sheave is caused to rotate in one direction or the other an amount which varies proportionately to the rise or fall of the float, and therefore to the change in water level. The rotary motion of the sheave is transmitted by suitable gearing to a lever arm 25 so that the arm moves up and down proportionally to variation in the water level, this gearing as shown comprising a worm wheel 8 fast on the shaft of the arm 1 and a worm 9 on the shaft of the sheave meshing with the worm wheel.

The arm I carries a contact 30 which is periodically engaged by a movable contact 3! carried by an arm 32 pivotally mounted to swing on an axis 33 of the arm I. The free end of the arm 32 is moved up and down in regular cycles by a motor driven cam 34 against which an antifriction roller on the end of the arm 32 normally rests under the weight of the arm. The cam 34 is most desirably heart shaped so that during one half of each revolution of the cam the arm 32 is raised at a constant angular velocity and during the other half of ach revolution of the cam the armis lowered t the same constant angular velocity, except so far as the movement of the arm may be limited by engagement of the contact 3| with the contact 30.

The contacts 30 and 3| are connected in an electric circuit which extends to the receiving device, and this circuit is thus closed once during each successive time interval in which the cam 34 makes one complete revolution, for a length of time or portion of such time interval which is determined by the position of the arm 25 and its contact 30. Each downward movement of the arm 32 continues until its contact 3| comes into engagement with the contact 30. Then during further rotation of the cam the arm 32 remains stationary and the circuit closing contact continues until the cam again comes into engagement with the roller on the end of the arm 32 and moves the arm upward and the contact ll away from the contact 30, thereby breaking the circuit. The length of time that the circuit is closed during each revolution will thus depend on the speed of revolution of the cam and the position of the arm 1. The speed of the cam being constant, if the arm 1 is moved upward;

the length of contactwill be proportionately increased, and if the arm I is moved downward, the length of contact will be proportionately decreased. The length of time during which the circuit is closed in each of said time intervals will thus vary proportionately with change in position of the arm I and therefore with change in position of the float 3 and therefore with change in the water level. If the speed of rotation of the cam should vary so as to cause a variation in the length of successive time intervals, then although the variation in the length of successive closed circuit periods due to change in position of the arm 25 will not beexactly proportionate to such changes in position of the'arm, nevertheless, the part of proportion of successive time intervals during which the circuit is closed will still vary proportionately to changes in position of the arm. The cam 34 is most desirably driven at a constant speed by any suitable actuating device or motor 36 such as a clock motor or a synchronous electric motor.

A scale 31 is desirably provided with which the end of the arm I cooperates as a pointer for showing the water level. This scale is principally useful in the calibration of a particular transmitting device with a particular receiver.

' Referring now to the receiving device as shown best in Figs. 4, and 6, the operative parts of the receiver are driven by a motor 40 and the operation of the receiver is controlled by an electro-magnetic device comprising an electro-magnet 4| connected in the circuit. The electromagnetic device determines the time during which the indicator-positioning movable members of the receiver are operated in each cycle of operations, and the speed of the motor determines the rate at which said movable members are moved. The motor is most desirably a constant speed motor such as a clock motor or a synchronous electric motor as shown. It is not necessary that the speed of the motor 40 or the speed of the motor 35 of the transmitting device be constant, but if the speed of either of these motors varies, then the speed of the other must vary proportionately so that the speed ratio between the two motors is maintained constant.

The motor 40 of the receiver drives continuously two drive rolls 42 and 43 in opposite directions at the same speed. 'These drive rolls are mounted in a movable frame or cage 44 which is pivotally mounted. in the main frame 45 of the receiving device to have a slight swinging movement about an axis at 46. The cage 44 comprises front and rear plates 41 and 48 connected by-rods 49. Plates 41 and 48 are cut away or of skeleton form to avoid interference with other parts of the apparatus. For driving the rolls 42 and 43, the motor, through a pinion 50 on its shaft, drives a gear 5| mounted on a shaft 52, the axis of which coincides with the axis about which the cage 44 swings. The shaft 52 has a pinion 53 fast thereon which meshes with and drives a gear 54 which is fast on the shaft of the driving roll 42. This gear 54 meshes with a gear 55 of the same size fast on the shaft of the driving roll 43. The driving rolls 42 and 43 will thus be driven by the motor in opposite directions at the same speed. As shown, the front and back plates of the frame or cage 44 are carried by two shouldered blocks 55 having pivot studs extending therefrom by which they are pivotally mounted in front and back plates of the main frame 45. The shaft 52, which carries the gear 5| and pinion 53, extends into pivot recesses in said blocks 56. s

The plate 41 of the cage 44 has a downwardly extending lower end which is slotted to receivean arm 50 extending from an armature 5| which is mounted to be attracted by the electro-magnet 4| and which when the magnet is deenergized is retracted to the position shown in Fig. 4 by a spring 52. When the magnet is energized the armature is attracted and moves the lower end of the cage 44 to the right in Fig. 4, thereby swinging the frame on its axis 46 to carry the driving roll 42 into engagement with the periphery of a disk which is mounted on and drives a shaft 1|, thereby rotating the disk and shaft in a clockwise direction as viewed in Fig. 4. When the magnet 4| is de-energized, the armature BI is retracted by the spring 52, and this movement of the armature swings the cage 44 in the opposite direction to move the driving roll 42 out of engagement with the disk 1|] and to carry the driving roll 43 into engagement with the periphery of a similar disk I2 which is mounted on and drives a shaft I3 which is co-axial with the shaft 1|, thereby rotating the disk-I2 .in a counterclockwise direction as viewed in Fig. 4..

The shaft ll carries an arm I5 fast thereon and also has connected to it a light coil spring 16 which tends to turn the shaft to hold the arm in a normal position of rest against an upwardly extending stop I1 and to swing the arm back to such position of rest after it has been moved therefrom. Similarly, the shaft 13 carries an arm 18 fast thereon and has connected to it a coiled spring 19 which tends to turn the shaft to hold the arm I8 against an upwardly extending stop and to return the arm to its position of rest against the stop after it has been moved away therefrom. The arms 15 and I8 constitute in the construction shown the two oppositely moving movable members of the receiver before referred to.

When the magnet 4| is energized and the cage 44 is thereby shifted to bring the driving roll 42 into engagement with the disk 10, the movable member or arm 15 will thereby be moved away from its stop 11 in a clockwise direction for a distance proportional to the time during which the electro-magnet remains energized; and when the magnet is de-energized and the cage swung in the opposite direction i move the roll 42 out of engagement with the disk 10 and the roll 43 into engagement with the disk I2, the shaft II will be rotated in the reverse direction by the spring 16 to swing the arm 15 back to its position of rest against the stop 11, and the arm 18 will be moved away from its stop 80 in a counterclockwise direction for a distance proportional to the time during which the magnet remains deenergized. Then when the magnet is again energized the disk 12 will be released and the spring 19 will rotate the shaft 13 to return the arm 13 to its position of rest, and the arm 15 will again be moved from its position of rest for a distance proportional to the time during which the magnet is energized; and these successive movements of the arms 15 and I8 will continue so long as the magnet is successively energized and de-energized. The driving means of the receiver, that is, the motor 40, is thus alternately connected to move first one and then the other of the arms 15 and I8.

As the circuit to the magnet 4| controlled by the transmitting device by which the connecting circuit I2 is, during each successive time interval in which the cam 34 makes one complete rotation, closed for a length of time whichvaries in successive time intervals proportionately with change in position of the moving member, the arm 25, of the transmitting device, the difference in length of successive movements of the arm of the receiver will vary proportionately with the changes in position of the movable member of the transmitter. As the successive lengths of time during which the circuit is open and the magnet de-energized vary inversely with variations in the length of time that the circuit is closed, the difference in length of successive movements of the arm l8 of the receiver will also vary proportionately with the changes in position of the movable member of the transmitter, but the difference in length of movement of the two positioning members i5 and 18 'will be in the reverse direction, that is, as the length of movement of one member increases the movement of the other will correspondingly decrease.

The indicating or effect-producing member of the receiver in the construction shown is an indicating and record marking pen arm I00 which is carried by a U-shaped member or yoke 85 pivotally mounted to swing about the axis of the aligned shafts H and iii. The outer ends of the shafts ll and 13 have their hearings in bearing blocks 81 which are set in plates 38 forming part of the main frame of the device and the outer ends of these blocks are shaped to form conical pivot points which extend into pivot openings in the arms of the yoke 85. There is suiiicient spring in the yoke to produce a pinching action on the pivot points so that when the yoke and indicating arm lull have been moved to any position they willstay in such position until force is applied to move them in one direction or the other. The intermediate or horizontal portion of the yoke 85 extends .between the arms 15 and 18, which are of sufiicient length so that they may come into engagement with the yoke when the moved from their respective positions of rest.

The stops TI and are positioned so that the distance between the positions of rest of the arms 15 and 18 is such that the movement of either ann if continued during the whole of one cycle of operations or one complete rotation of the cam 34 would move the yoke into engagement with the other arm. When, therefore, the magnet 4| is energized and the arm 15 thereby caused to be moved from its position of rest in a clockwise direction, if the yoke is in a position such that it will be engaged by the arm before the arm has completed its movement, the yoke will be moved in a clockwise direction by the arm to carry the indicating arm I5 to a position corresponding to the position of the movable member of the transmitter. Likewise, when the magnet is de-energized and the arm 18 thereby caused to be moved in a counter-clockwise direction, if the yoke is in a position to be engaged by the arm before the latter has completed its movement, it will be moved to carry the indicating arm Hill in a counter-clockwise direction to a position corresponding to the position of the movable member of the transmitter.

So long as the movable member of the trans-' the yoke and then return to their positions of rest. This position of the yoke and of the indicating arm will then correspond to the position of the movable member of the transmitter. When, however, any movement of the movable member of the transmitter occurs resulting in an increase in the length of time during which the electric circuit is closed, the arm 75 .will make a longer movement and the arm 18 a shorter movement, and the yoke and indicating arm will be moved to the right or in a clockwise direction a distance corresponding to the change in position of the movable member of the transmitter. Likewise, if the movable member of the transmitter moves in the direction to decrease the circuit closing period, the arm 15 will move a lesser and the arm 18 a greater distance and the indicating arm will be moved a distance to the left or counter-clockwise proportional to the change in position of the movable member of the transmitter. When the apparatus shown is used for indicating change in water level, the indicating arm or pointer I00 will move to the right when the water level rises and to the left when the water level drops.

There will thus be an operation of the receiving device for adjusting the position of the indicating arm I00 during each revolution of the cam 34 of the transmitting device. So long as the position of the movable member of the transmitter does not change, the indicating arm will not be moved, but whenever there is a change in position of the movable member of the trans.- mitter between successive time intervals or revolutions of the transmitter cam, the indicating arm of the receiver will be moved for a distance proportional to, and in the direction corresponding to, the change in position of the movable member of the transmitter.

The frequency of the cycle of operations, or length of said successive time intervals, may be varied widely and may be made as desired to suit the requirements of any particular installation. I have found 10 second intervals, or 6 cycles a minute, convenient and satisfactory for an instrument such as shown for indicating changes in water level and the like. Shorter intervals or much longer intervals, such as intervals of one hour duration, might be used and be found satisfactory for some purposes. For transmitting the movement of a more or less constantly changing member, the shorter the time interval in which successive operations take place the more accurate will be the indication made by the receiver.

In order to prevent damage to the instrument through improper adjustment or failure in the periodic opening and closing of the connecting electric circuit, a friction connection is provided between the disks l0 and 12 and the respective arms 75 and I8. Such connection is provided in the construction shown by a friction connection between each of the disks l0 and-l2 and the shaft on which it is mounted.

In describing the transmitter, it has been referred to as operating to close the circuit l2 for a part of each time interval. It might equally be considered as operating to-open the circuit for a part of each successive time interval. And in the receiver, an obvious equivalent of the particular arrangement shown would be one in which the movement and effect resulting in the ar-' 0 rangement shown frcm the closing of the circuit 7 and the energizing of the magnet 4| result from opening the circuit and de-energizing the magnet; and in which closing the circuit causes the movement and effect which in the arrangement clutch II in the receiver must respond in close shown results from opening the circuit. It is desired to point out, however, that the principle of my invention is not limited to the particular form of telemetershown as it is applicable to other systems employing time as the basis for transmitting measurements or proportional movements, within the scope of the claims appended hereto.

The transmitting and receiving stations are connected by a single two-conductor line it which carries both alternating and direct current, both of which, in the arrangement shown, are taken from an alternating current power line I through a transformer ii. Though not necessary, it is usually desirable to connect to the power line through a transformer. It serves to insulate the telemetering line from the power line, and makes it possible to step the line voltage either up or down to any desired voltage.

Assuming, now, that the maximum allowable potential of 120 volts is obtainable from the secondary of the insulating transformer I I, alternating current flows in the following circuit; from one side of the secondary winding of the transformer ll through a connecting wire I2 containing a by-pass condenser IS, the capacity-of which at this voltage being not in excess of 1 microfarad, to one side of the line Ill and then through one side of the part Ilia of the line III which extends from the place of the supply of current to the transmitter. At the transmitter. the alternating current passes through the motor 36 and thence through a .3 microfarad condenser I4, and back through the other side of the part We of the line l0, through the filter condenser l5 and the connecting line l6 to the other side of the secondary of the transformer II. A part of the alternating current supplied by the 1 microfarad condenser l3 fiows through one side of the part "lb of the line "I which extends from the place of current supply to the receiver 13, flowing through the .3 microfarad condenser H to the motor b and thence to the other side of the line I01) and back through the connecting line it to the other side of the secondary winding of the transformer ii.

The path of the direct current is as follows: Alternating current at a potential of 120 volts is supplied by the secondary winding of the transformer II to one side of a rectifier 20, and the rectified direct current suitably smoothed by action of the filter condenser Ii, which may, for

instance, have a capacity of 5 microfarads, flows through a connecting wire 2| and one side of the line ill to the transmitting station A. Assuming that the contacts of the make and break device 30 and 3| are closed, the direct current flows through the conductor 22 and the choke coil 23, which may'with the impressed voltage under discussion have an inductance of 100-200 henrys,

thence through the now closed contacts 30 and 3| and the conductor 24 back through the other side of the line III to the receiver, where it passes through the choke coil 25 which may be of similar inductance to 23 and thence through the windings of the clutch relay ll back to the other side of the secondary of the transformer Ii via one side of the line l0 and the conductor I. The windings of the clutch or relay ll are preferably so proportioned that the direct current required to suitably energize this device will never be greater than watt, thus keeping at a minimum losses due to line resistance.

In a telemetering system whereby transmission of measurements is based on time, the relay or synchronization with the opening and closing of the contacts 30 and 3| in the transmitting instrument. If practically instantaneous response of relay II is not obtained, an error will be introduced in the recording of the time impulses which in turn will be translated into an erroneous reading on the chart of the recorder of the receiver.

Reference to the drawings will disclose that the condensers I3, I4 and IT parallel the windings of the relay coil ll though certain amounts of resistance are placed in series with these capacitances by the windings of the resonance motors, the inductance 25, the secondary winding of the transformer i I and the variable resistance 21,

which tend to retard both their charging and discharging. As the Wallace resonance motor requires a maximum power input not exceeding 1 watt, relatively small values of capacitance can be employed for passing suflicient alternating current to run the motors, and therefore, even with a relay winding of such high inductance as to require only V watt for its eflicient operation, the lag introduced into its action by means of these small capacitances will be insuflicient to cause any noticeable error in the reading of the recorder B.

It will be noted that while the line l0, except at its ends, carries both alternating current and direct current, at each end of the line the two currents are separated by the choke coils 23 and 2' in the direct current branches of the circuit and by the condensers H and H in the alternating current branches leading to the motors.

The rectifier 20 as shown may be a copper oxide rectifier, but any suitable rectifier might be used, including the vacuum tube rectifier. The condenser acts as a smoothing condenser, that is to say, it equalizes to a degree the fiow of direct current through the system. It also prevents short circuiting of the direct current. A second smoothing condenser 20 may, if desired, be provided shunted around the clutch or relay winding ll. If this condenser 26 is not provided, the clutch or relay winding ll may serve to prevent 'the passage of alternating current. Adjustable resistances 21 and 28 may be provided as shown in the alternating current supply connection l2 and the direct current supply connection 2|, respectively, for adjusting the alternating current and direct current voltages in the line.

The alternating and direct currents may be supplied to the line II at the transmitting end of the line or at the receiving end of the line. or at any intermediate point. When the point of power supply is practically at the transmitter or receiver, then the alternating current driving motor at the transmitter or receiver, as the case may be, can be of the usual synchronous motor type instead of a resonance motor or other low power consumption device. and may be supplied with power by being independently connected direct to the power line I Instead of being a two-wire line, the two-conductor connecting circuit may use the earth as one of the conductors or as a portion of one.

It is usually most desirable to derive the direct current from the supply line from which the alternating current is derived, but a different source of direct current, such as a storage or other battery, may beused in which case the battery will take the place in the circuit of the rectifier-20.

Since the two driving motors, one at the transmitting end and the other at the receiving end,

are in parallel with each other across the parts Illa and lob of the connecting line H], any inequality in line drop from the point of power supply to the two line parts Illa and lb may, if necessary, be compensated for by proper resistances in series with the motor windings only. Instead of resistances for this purpose in the alternating current branches at the transmitting and receiving stations, the alternating current may be supplied to the transmitter supplying portion Illa and to the receiver supplying portion Nb of the line H), as shown in Fig. 2, through separate connecting wires 30a and 30b which connect to the line H] on either side of a choke coil 3i, each of these connecting wires 30a and 3012 being pro vided with a resistance 21a and 211), respectively, which is preferably adjustable.

What is claimed is:

1. A telemetering system, comprising a transmitting apparatus and a receiving apparatus connected by a two-conductor line; means for supplying direct current to said line; the transmitting apparatus including an alternating current motor which operates in synchronism with the current by which it is driven and means driven thereby for variably controlling the direct current flowing over said line; the receiving apparatus including indicating mechanism, an alternating current motor which operates in synchronism with the current by which it is driven for driving the indicating mechanism, and means responsive to changes in the direct current in said line for controlling the operation of the indicating mechanism by its motor; and means for supplying alternating current to said line from a source distant from one of said apparatus; a choke and a low capacity condenser being provided at said apparatus distant from the source of alternating current for separating the direct and alternating currents, and the driving motor of said apparatus distant from the source of alternating current being operated by the alternating current flowing in said line and being a motor which operates on an alternating current with a power input not greatly in excess of one watt to enable a low capacity condenser to be used to filter out the direct current and thereby reduce to a minimum the time lag of the said means responsive to changes in the direct current, and the driving motor of the other apparatus being driven by current derived from said source current.

2. A telemetering system, comprising a transmitting apparatus and a receiving apparatus connected by a two-conductor line, means for supplying alternating current to said line at a point more distant from one of said apparatus than from the other, and means for supplying direct current to said line; the transmitting apparatus including a member the position of which varies with variations in the condition tobe transmitted, and a motoredriven circuit-controlling device for variably controlling the direct current in said line according to the position of said member, and an alternating current motor which operates in synchronism with the current by which it is driven for driving said circuit-controlling device; the

of alternating receiving apparatus including indicating means,

and an alternating current motor which'operates in synchronism with the current by which it is driven for driving the indicating means, and means controlled by the direct current in said line for controlling the operation of the indicating means by its driving motor; a choke and a W capacity condenser being provided at the more distant apparatus for separating the direct and alternating currents, and the driving motor of the more distant apparatus being operated by the alternating current flowing in said line and being a motor which operates on a current of not over 5 milli'amperes at under volts to enable a low capacity condenser to be used to filter out the direct current and thereby reduce to a minimum the time lag of the said means controlled by the direct current, and the driving motor of the other apparatus being operated by current derived from the same source of alternating current as said more distant apparatus.

3, A telemetering system, comprising a twoconductor line, means for supplying alternating current to said line, means for supplying direct current to said line, means at a transmitting station at one end of the line operated by a motor driven in synchronism with the alternating current in said line for varying the length of the periods of flow of direct current, indicating means at a receiving station at the other end of the line, and means at said receiving station for controlling the indicating means according to the length of the periods of flow of direct current in the line including a motor driven in synchronism with the alternating current in said line and a clutch controlled by the flow of direct current in said line, one of said stations being distant from the point of supply of alternating current to said line, a choke and a low capacity condenser being provided at said distant station for separating the alternating and direct currents, and the motor at said distant station being a resonance motor driven by the alternating current flowing in said line and operating on a current of not over 5 milliamperes at under 120 volts to enable a low capacity condenser to be used to filter out the direct current and thereby reduce to a minimum the time lag of said clutch.

4. A telemetering system, comprising a twoconductor line, means for supplying alternating current to said line, means for supplying direct current to said line, means at a transmitting station at one end of the line operated by a motor driven in synchronism with the alternating current in said line for varying the length of the periods of flow of direct current, indicating means at a receiving station at the other end of the line, and means at said receiving station for controlling the indicating means according to the length of the periods of flow of direct current in the line including a motor driven in synchronism with the alternating current in said line and a clutch controlled by the fiow of direct current in said line, one of said stations being distant from the point of supply of alternating current to said line, a choke and a low capacity condenser being provided at said distant station for separating the alternating and direct currents, and the motor at said distant station being driven by the alternating current flowing in said line and being one which has a power consumption below 300 milli- Watts to enable a low capacity condenser to be used to filter out the direct current and thereby reduce to a minimum the time lag of said clutch.

5. A telemetering system, comprising a transmitting appparatus and a receiving apparatus connected by a two-conductor line, means for supplying alternating current to said line at a point distant from each of said apparatus, and means for supplying direct current to said line;

the transmitting apparatus including an alteruthe receiving apparatus nating current motor driven by and in synchronism with the alternating current flowing in said line, and means driven by said motor for variably controlling the direct current flowing in said line; including indicating mechanism, an alternating current motor driven by and in synchronism with the alternating current flowing in said line for driving the indicating mechanism, and means responsive to changes in the direct current in said line for controlling the operation of the indicating mechanism by its motor; a choke and a low capacity condenser being provided at the transmitting apparatus and at the receiving apparatus for separating the direct and alternating currents; and each of said driving motors being a motor which has a power consumption not greatly in excess of one watt to enable low capacity condensers to be used to filter out direct current and thereby reduce to a mini- 1 mum the time lag of said means responsive tc changes in the direct current.

CHARLES F. WALLACE. 

